Reaching soil cleanup levels by vapor extraction: laboratory approach

摘要

Nonaqueous phase liquids (NAPLs) such as gasoline and chlorinated solvents have a very low water solubility. When these compounds enter the unsaturated soil, buoyancy and capillary forces may hold a portion of them is the soil pores as residual saturation. Hoag and Marly have reported 12-20 percent residual saturation for gasoline in a partially water saturated sand~.1 Soil Vapor Extraction (SVE) is a technique that removes volatile and some semi-volatile organic compounds from the unsaturated soil by induced flow of air~(2, 3). Through contacts with each state's EPA office, it was concluded that 21 states have their own regulations for soil cleanup levels and the others follow the guidelines set forth by the Federal RCRA and CERCLA regulations~4. The State of Connecticut Department of Environmental Protection (DEP) requires contaminated. soils to be remediated to a level such that the amount of contaminant partitioning into the liquid phase remains below the drinking water standard, under equilibrium condition. These standards are 0.001 mg/L for benzene, 1 mg/L for toluene, 0.7 mg/L for ethyl benzene, and 0.005 mg/L for trichloroethylene and tetrachloroethylene.~5 In order to determine the amount of volatile organics that partition into the liquid phase a test called Toxic Characteristics Leaching Procedure with Zero Headspace Extraction (TCLP-ZHE) is applied to contaminated soils. This test determines the amount of VOC that would partition into the liquid phase in the TCLP-ZHE procedure.